1. Field of the Invention
The present invention relates to a system, method, and program for analyzing and selecting channel paths to a device.
2. Description of the Related Art
Host computer systems may perform input/output (I/O) operations against a storage unit, such as a Direct Access Storage Device (DASD), which is comprised of numerous interconnected hard disk drives (HDDs) that form a single mass storage space. In such systems, a storage controller, also referred to as a control unit, manages input/output (I/O) operations between the host systems and the DASD. Examples of control units include the International Business Machines (“IBM”) Enterprise Storage Server, described in the publication “IBM Enterprise Storage Server: Introduction and Planning Guide”, IBM document no. GC26-7294-02 (IBM Copyright, November 1999) and the IBM 3990 Storage Controller, described in IBM publication, “IBM 3990 Storage Control Reference (Models 1, 2, and 3), IBM document no. GA32-0099-06 (Copyright IBM Corp. 1988, 1994), which publications are incorporated herein by reference in its entirety.
The hosts include a channel subsystem that directs the flow of data between the host main storage and the storage controllers. In current implementations, each host may have up to 256 channels. Each channel is identified by a channel path identifier (CHPID). A channel comprises a host adaptor into which a cable is connected that leads directly to an interface port on the storage controller or a port in a switch that links to the storage controller. A channel path comprises the physical connection from a host adaptor to a port on a switch, such as an ESCON director, and the connection from another port on the same switch to an interface port in the control unit. In current implementations, a channel path in the host may be dynamically assigned to one physical path comprising the connection links from the host adaptor to the switch port, and then from another port on the same switch to the interface port in the control unit. The commonly assigned and co-pending U.S. patent application Ser. No. 09/407,544, entitled “Method, System, and Program Products for Managing I/O Configurations of a Computing Environment” filed on Sep. 28, 1999 by P. B. Yocom, H. M. Yudenfriend, W. J. Rooney, Richard Cwiakala, which patent is incorporated herein by reference in its entirety, describes an architecture for allowing the dynamic assignment of channel paths in the host to different physical paths from the host to the control unit.
The above patent mentions that one goal of dynamically assigning host channel paths to a physical path is to find the path assignment for a channel path that provides the best availability, i.e., avoids any single point of failures. For this reason, there is a need in the art to determine the path that optimizes the overall availability of all the paths to the storage controller.